Co genetic Cr-bearing tourmaline and emerald in the Novo Cruzeiro pegmatite field (Minas Gerais, Brazil)

Abstract

The Novo Cruzeiro pegmatite field in Minas Gerais (Brazil), located between Téofilo Otoni and the Jequitinhonha River, belongs to the areas of the EBPP with tourmaline and emerald occurrences. The pegmatites show beside of coloured tourmalines, Cr-rich black tourmaline cogenetic with Cr-bearing emerald. General crystallization conditions of pegmatites show, based on the obtained data, important changes during the final phase of tourmaline crystallisation which caused variations in tourmaline chemistry and reflects differences in the chemistry of the participating fluids. The crystallization of tourmaline ceased and after a period of co-crystallization, emerald was the only formed mineral. The obtained information suggests a crystallization sequence from tourmaline over tourmaline+emerald to emerald. A part of B and Fe may come from the host rock, Be and B from the intrusive granites and Cr from regional mafic to ultramafic rocks like amphibolite or Bt-Qz-schist.